Wellbore tractor with fluid conduit sheath

ABSTRACT

A fluid conduit sheath for a wellbore tractor can provide transportation of a working fluid external to a wellbore tractor in a downhole environment. The fluid conduit sheath can further provide cooling to electrical devices in the wellbore tractor. The fluid conduit sheath can be configured to be disposed around the body of the wellbore tractor, defining a fluid conduit between the sheath and the wellbore tractor. Spacers can be used to maintain the position of the sheath relative to the tractor and also to couple the tractor to the sheath. The fluid conduit sheath can be advantageous in tractors whose internal components substantially preclude the use of an internal fluid conduit, such as tractors with electrically-actuated grippers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates generally to downhole tools and more specifically to devices, systems, and methods for transporting fluids in connection with downhole tools.

2. Description of the Related Art

Tractors for moving within underground boreholes are used for a variety of purposes, such as oil drilling, mining, laying communication lines, and many other purposes. In the petroleum industry, for example, a typical oil well comprises a vertical borehole that is drilled by a rotary drill bit attached to the end of a drill string. The drill string may be constructed of a series of connected links of drill pipe that extend between ground surface equipment and the aft end of the tractor. Alternatively, the drill string may comprise flexible tubing or “coiled tubing” connected to the aft end of the tractor. A drilling fluid, such as drilling mud, is pumped from the ground surface equipment through an interior flow channel of the drill string and through the tractor to the drill bit. The drilling fluid is used to cool and lubricate the bit, and to remove debris and rock chips from the borehole, which are created by the drilling process. The drilling fluid returns to the surface, carrying the cuttings and debris, through the annular space between the outer surface of the drill pipe and the inner surface of the borehole.

Tractors for moving within downhole passages are often required to operate in harsh environments and limited space. For example, tractors used for oil drilling may encounter hydrostatic pressures as high as 16,000 psi and temperatures as high as 300° F. Typical boreholes for oil drilling are 3.5-27.5 inches in diameter. Further, to permit turning, the tractor length should be limited. Also, tractors must often have the capability to generate and exert substantial force against a formation. For example, operations such as drilling require thrust forces as high as 30,000 pounds.

As a result of the harsh working environment, space constraints, and desired force generation requirements, downhole tractors are used only in very limited situations, such as within existing well bore casing. While a number of the inventors of this application have previously developed a significantly improved design for a downhole tractor, further improvements are desirable to achieve performance levels that would permit downhole tractors to achieve commercial success in other environments, such as open bore drilling.

Western Well Tool, Incorporated has developed a variety of downhole tractors for drilling, completion and intervention processes for wells and boreholes. For example, the Puller-Thruster Tractor is a multi-purpose tractor (U.S. Pat. Nos. 6,003,606, 6,286,592, and 6,601,652) that can be used in rotary, coiled tubing and wireline operations. A method of moving is described in U.S. Pat. No. 6,230,813. The Electro-hydraulically Controlled Tractor (U.S. Pat. Nos. 6,241,031 and 6,427,786) defines a tractor that utilizes both electrical and hydraulic control methods. The Electrically Sequenced Tractor (U.S. Pat. No. 6,347,674) defines a sophisticated electrically controlled tractor. The Intervention Tractor (also called the Tractor with improved valve system, U.S. Pat. No. 6,679,341 and U.S. Patent Application Publication No. 2004/0168828) is preferably an all hydraulic tractor intended for use with coiled tubing that provides locomotion downhole to deliver heavy loads such as perforation guns and sand washing. A tractor using an Expandable Ramp Gripper, which can incorporate the use of a plurality of interconnected links to produce a dual radial force mechanism is described in U.S. Provisional Patent Application No. 60/781,885. Each of the foregoing patents and patent applications is incorporated by reference herein in its entirety.

These various tractors are intended to provide locomotion, to pull or push various types of loads. For each of these various types of tractors, various types of gripper elements have been developed. Thus an important part of the downhole tractor tool is its gripper system.

In one known design, a tractor comprises an elongated body, a propulsion system for applying thrust to the body, and grippers for anchoring the tractor to the inner surface of a borehole or passage while such thrust is applied to the body. Each gripper has an actuated position in which the gripper substantially prevents relative movement between the gripper and the inner surface of the passage, and a retracted position in which the gripper permits substantially free relative movement between the gripper and the inner surface of the passage. Typically, each gripper is slidingly engaged with the tractor body so that the body can be thrust longitudinally while the gripper is actuated. The grippers preferably do not substantially impede “flow-by,” the flow of fluid returning from the drill bit up to the ground surface through the annulus between the tractor and the borehole surface.

Tractors may have at least two grippers that alternately actuate and reset to assist the motion of the tractor. In one cycle of operation, the body is thrust longitudinally along a first stroke length while a first gripper is actuated and a second gripper is retracted. During the first stroke length, the second gripper moves along the tractor body in a reset motion. Then, the second gripper is actuated and the first gripper is subsequently retracted. The body is thrust longitudinally along a second stroke length. During the second stroke length, the first gripper moves along the tractor body in a reset motion. The first gripper is then actuated and the second gripper subsequently retracted. The cycle then repeats. Alternatively, a tractor may be equipped with only a single gripper for specialized applications of well intervention, such as movement of sliding sleeves or perforation equipment.

Grippers may be designed to be powered by fluid, such as drilling mud in an open tractor system or hydraulic fluid in a closed tractor system. Typically, a gripper assembly has an actuation fluid chamber that receives pressurized fluid to cause the gripper to move to its actuated position. The gripper assembly may also have a retraction fluid chamber that receives pressurized fluid to cause the gripper to move to its retracted position. Alternatively, the gripper assembly may have a mechanical retraction element, such as a coil spring or leaf spring, which biases the gripper back to its retracted position when the pressurized fluid is discharged. Motor-operated or hydraulically controlled valves in the tractor body can control the delivery of fluid to the various chambers of the gripper assembly.

In other tractor configurations, grippers are designed to be actuated by electric motors. The electric motors operate by rotating an output shaft coupled to the gripper to move the gripper between its retracted position and its actuated position. Often, tractors including electric motors include other electronic components, such as processor-based control systems to control the sequenced operation of the grippers described above. The electric motors and components must be configured to withstand the high temperatures and pressures often encountered in downhole environments.

In addition to the drilling fluid or hydraulic fluid noted above, various downhole operations can require a supply of working fluid. For example, sand working, equipment manipulation, setting patches, milling, logging and perforating, and displacing fluid or slurry are typically performed with a working fluid. This working fluid must be transported downhole. In tractors with fluid powered grippers, the fluid used for gripper actuation can be used in downhole operations in addition to powering the grippers. However, tractors having electrically actuated grippers often lack the ability to transport fluid for use in downhole operations.

SUMMARY OF THE INVENTION

In various embodiments, a tractor including a fluid conduit sheath, a fluid conduit sheath, and a method for transporting fluid are provided. The embodiments discussed herein overcome the shortcomings of prior tractors and provide transportation of a working fluid downhole for use in downhole operations. This external fluid conduit for transportation of working fluid downhole can be integrated into an existing tractor, such as one having electrically-actuated grippers. This working fluid can also be used to cool electric motors and other electronic components of a tractor.

In some embodiments, a tool for moving within a passage is provided. The tool comprises: an elongate body having an outer surface; at least one gripper assembly engaged with the body; an actuator; and a fluid conduit sheath disposed around at least a portion of the elongate body. The gripper assembly has an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface. The gripper assembly has a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage. The actuator is configured to move the gripper between the actuated position and the retracted position. The fluid conduit sheath has an inner surface such that the fluid conduit sheath defines a fluid conduit between the outer surface of the elongate body and the inner surface of the fluid conduit sheath.

In other embodiments, a sheath for use with a tool for moving within a passage is provided. The sheath comprises a sheath body and at least one spacer configured to separate the tool and the sheath body. The sheath body has an inner surface. The sheath body is configured to be disposed around the tool such that the sheath body defines a fluid conduit between an outer surface of the tool and the inner surface of the sheath body. The spacer is configured to maintain the position of the tool with respect to the sheath body.

In other embodiments, a method of transporting fluid downhole in a tool for moving within a passage is provided. The method comprises providing a tool for moving within a passage, the tool comprising a fluid conduit sheath defining a fluid conduit; and transporting fluid through the fluid conduit. The tool comprises: an elongate body having an outer surface; at least one gripper assembly; and the fluid conduit sheath. The gripper assembly is engaged with the body. The gripper assembly has an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface. The gripper assembly has a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage. The fluid conduit sheath is disposed around at least a portion of the elongate body. The fluid conduit sheath has an inner surface such that the fluid conduit sheath defines a fluid conduit between the outer surface of the elongate body and the inner surface of the fluid conduit sheath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of tool for movement within a passage having a fluid conduit sheath;

FIG. 2 is a schematic diagram of a longitudinal cross section of the tool of FIG. 1;

FIG. 3 is a cross sectional view of the tool of FIG. 1 taken along line 3-3;

FIG. 4 is a cross-sectional view of the tool of FIG. 1 taken along line 4-4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1 and 2, one embodiment of tool for movement within a passage is shown. The tool can be a downhole tractor 10 having an elongate body 12 and at least one gripper assembly 14. In the illustrated embodiment, the downhole tractor 10 includes two gripper assemblies 14. It is contemplated that in other embodiments, the tool can comprise more than two gripper assemblies 14. The tool further comprises an actuator 16 operatively coupled to at least one of the gripper assemblies 14. In the illustrated embodiment, each gripper assembly 14 is operatively coupled to a corresponding one actuator 16. It is contemplated that in other embodiments, a single actuator 16 can be coupled to more than one gripper assembly 14. The tool further comprises a fluid conduit sheath 18 disposed around at least a portion of the elongate body 12.

In the illustrated embodiment, the fluid conduit sheath 18 has an inner surface 20. The fluid conduit sheath 18 defines a fluid conduit 22 between an outer surface 24 of the elongate body 12 and the inner surface 20 of the fluid conduit sheath. A working fluid such as a hydraulic fluid or other fluid for sand washing, setting patches, sampling fluids, milling, logging and perforating, or fluid and slurry displacement can be transported through the fluid conduit 22. A pump or other fluid transport device can be used to transport the working fluid in the fluid conduit. In some embodiments, the fluid transport device can be positioned in the tractor 10, while in other embodiments, the fluid transport device can be located on the outside of the wellbore.

In the embodiments illustrated in FIGS. 1 and 2, the fluid conduit sheath 18 comprises a generally cylindrical sheath body 26 having a generally circular cross sectional profile that is disposed around a generally cylindrical elongate body 12 of the downhole tool. In other embodiments, it is contemplated that the sheath body 26 could have different cross-sectional configurations, for example, the sheath body could having a generally oval cross sectional profile, a generally triangular cross-sectional profile, a generally square cross-sectional profile, or another shape. In some embodiments, the shape of the sheath body 26 can be selected to fit within or travel easily within a wellbore having a known geometry.

Desirably, the material of the sheath body 26 is selected and sized to withstand the adverse temperature and pressure conditions that can be encountered by a tractor in a downhole environment. Uphole of the tractor body, the sheath body 26 can be a different material such as a semi rigid material allowing the tractor to advance around bends or other obstacles substantially without the sheath body 26 binding (as is possible with a rigid sheath body) or crimping (as is possible with a flexible sheath body). Uphole of the tractor body, wireline, coiled tubing 27, other control cables, wires, tethers, or other devices can run inside the sheath body 26 to operatively couple the tractor 10 to a surface location.

With reference to FIGS. 3 and 4, the sheath body 26 can be configured to allow passage of the gripper assembly 14 therethrough when the gripper assembly is in an actuated configuration. As illustrated in FIG. 3, the sheath body 26 comprises a first segment 30 defined by a substantially cylindrical profile configured to be disposed around substantially the entire circumference of the elongate body 12. As noted above, in other embodiments, the cross-sectional profile of the first segment can be other than circular. The external fluid conduit 22 thus allows a working fluid to be delivered by a tractor 10 whose internal space constraints would substantially preclude transport of fluid internally.

With reference to FIG. 4, the sheath body 26 further comprises a second segment 32 configured to allow passage of the gripper assembly 14 when the gripper assembly 14 is in its actuated position. In the illustrated embodiments, a gripper assembly 14 comprises three gripper arms 28. As illustrated, the second segment 32 of the sheath body 26 comprises three apertures 34, each sized and configured to allow the passage of a corresponding gripper arm 28. In the second segment, the fluid conduit 22 defined by the sheath body 26 is thus divided by the apertures 34 into three flow areas extending between each pair of adjacent gripper arms 28. Each of the flow areas can have a pair of side walls to sealingly couple the fluid conduit sheath 18 to the tractor 10 such that the working fluid is retained in the fluid conduit 22. It is contemplated that in different embodiments of tractor, gripper assemblies 14 can have more or fewer than three gripper arms 28 and the fluid conduit sheath 18 can have correspondingly more or fewer apertures 34 and flow areas.

In the illustrated embodiments, the gripper assemblies 14 include linkage based gripper arms 28, however, it is contemplated that in other embodiments, the tractor can have different gripper configurations, such as continuous beam grippers or inflatable bladder grippers. In these embodiments, the second segment 32 of the fluid conduit sheath can have apertures 34 sized and configured to allow the gripper assemblies to be actuated.

With reference to FIG. 3, the tractor can include one or more spacers 36 separating the outer surface of the elongate body 12 from the inner surface of the fluid conduit sheath 16. The spacers 36 can maintain the position of the fluid conduit sheath 18 relative to the elongate body of the tractor 10 such that the fluid conduit defined thereby has a substantially constant area. The spacers 36 can also couple the fluid conduit sheath 18 to the tractor 10. In the illustrated embodiments, the spacers 36 maintain the fluid conduit sheath substantially concentrically disposed about the tractor 10, although in other embodiments, it is contemplated that the spacers 36 can be configured to position the fluid conduit sheath 18 such that a longitudinal axis of the fluid conduit sheath 18 is offset from a longitudinal axis of the tractor 10.

With reference to FIG. 2, the actuator 16 for the gripper assembly 14 may be an electric motor positioned within the elongate body 12. In the illustrated embodiment, the electric motor drives an output shaft which is operatively coupled to the gripper assembly 14. It is contemplated that in other embodiments, the actuator can be a hydraulic piston or fluid turbine actuator. In some embodiments, the tractor 10 can include other electrical devices, such as processor devices to control valve sequencing or motor operations. In view of elevated temperatures that can be encountered by the tractor 10 in a downhole environment, these electrical motors and devices can become damaged and unreliable after relatively short downhole operational time, requiring maintenance or replacement. This overheating of electrical components can be especially pronounced in tractors having electric motor actuators as they often do not include potentially heat dissipating internal fluid conduits to transport fluid for use in hydraulic actuators. Advantageously, however, the flow of fluid through the fluid conduit defined by the fluid conduit sheath 18 can cool these electrical motors and components. In some embodiments, the fluid conduit sheath 18 can be sized and configured such that the fluid conduit can transport a desired volumetric flow rate of working fluid to provide a predetermined amount of cooling for electrical components. In some embodiments, the spacers 36 can be shaped and positioned to direct a flow of working fluid in the fluid conduit towards electrical devices. Thus, transport of the working fluid within the fluid conduit sheath can extend the duty cycles of various electrical devices in a tractor 10.

While the illustrated embodiments depict a tractor 10 including a fluid conduit sheath 18, in other embodiments, a fluid conduit sheath 18 can be applied as a retrofit to a tractor. The fluid conduit sheath 18 can be configured to be disposed around existing and future tractor and gripper configurations of Schlumberger, Welltec, Expro Americas, Inc., Aker Kvaerner, or other downhole tractor designers and manufacturers. The cooling and fluid transport advantages can be highly desirable on tractors including centrally mounted electrical motors or turbines that would substantially prevent fluid flow through an internal conduit. However, the fluid conduit sheath can also be used in a tractor having hydraulically actuated gripper assemblies. In these tractors, the addition of a fluid conduit sheath as described herein can provide fluid transportation to perform various downhole operations, and increase equipment lifespan through cooling.

A tractor and fluid conduit sheath such as the one described herein can be used in various embodiments of a method to transporting fluid downhole. The method can include the steps of providing a tractor including an elongate body, a gripper, and a fluid conduit sheath disposed around the elongate body and defining a fluid conduit therebetween, and transporting fluid through the fluid conduit external to the elongate body. In some embodiments, the method can include the steps of determining a cooling requirement for an electrical device, and configuring the fluid conduit sheath to have sufficient cooling capacity to meet the cooling requirement.

Although these inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. Further, the various features of these inventions can be used alone, or in combination with other features of these inventions other than as expressly described above. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow. 

1. A tool for moving within a passage, comprising: an elongate body having an outer surface; at least one gripper assembly engaged with the body, the gripper assembly having an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface, the gripper assembly having a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage; an actuator configured to move the gripper between the actuated position and the retracted position; and a fluid conduit sheath disposed around at least a portion of the elongate body and having an inner surface such that the fluid conduit sheath defines a fluid conduit between the outer surface of the elongate body and the inner surface of the fluid conduit sheath.
 2. The tool of claim 1, wherein the elongate body has a circumference and the fluid conduit sheath comprises: a first segment defined by a substantially cylindrical profile disposed around substantially the entire circumference of the elongate body; and a second segment configured to allow passage of the gripper assembly therethrough when the gripper assembly is in the actuated position.
 3. The tool of claim 1, further comprising a spacer separating the outer surface of the elongate body and the inner surface of the fluid conduit sheath.
 4. The tool of claim 1, further comprising a plurality of spacers separating the outer surface of the elongate body and the inner surface of the fluid conduit sheath.
 5. The tool of claim 1, wherein the actuator comprises a motor configured to be powered by electricity.
 6. The tool of claim 5, wherein the fluid conduit sheath is configured to direct fluid near the motor to cool the motor.
 7. The tool of claim 1, further comprising coiled tubing.
 8. A sheath for use with a tool for moving within a passage, the sheath comprising: a sheath body having an inner surface, the sheath body configured to be disposed around the tool such that the sheath body defines a fluid conduit between an outer surface of the tool and the inner surface of the sheath body; and at least one spacer configured to separate the tool and the sheath body to maintain the position of the tool with respect to the sheath body.
 9. The sheath of claim 8, wherein the tool comprises an elongate body and a gripper assembly, the gripper assembly having an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface, the gripper assembly having a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage; and wherein the sheath body comprises: a first portion configured to be disposed around the elongate body; and a second portion configured to allow passage of the gripper assembly therethrough when the gripper assembly is in the actuated position.
 10. The sheath of claim 9, wherein the gripper assembly comprises three gripper arms and wherein the second portion of the sheath body comprises three apertures, the apertures sealed with respect to the tool such that fluid is retained in the fluid conduit, and each of the apertures configured to permit passage of a corresponding gripper arm therethrough when the gripper assembly is in the actuated position.
 11. The sheath of claim 9, wherein the sheath is comprised of a material selected to withstand elevated temperatures in the passage.
 12. A method of transporting fluid downhole in a tool for moving within a passage, the method comprising: providing a tool for moving within a passage, the tool comprising: an elongate body having an outer surface; at least one gripper assembly engaged with the body, the gripper assembly having an actuated position in which the gripper assembly grips onto an inner surface of the passage to substantially limit relative movement between the gripper assembly and the inner surface, the gripper assembly having a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and the inner surface of the passage; a fluid conduit sheath disposed around at least a portion of the elongate body and having an inner surface such that the fluid conduit sheath defines a fluid conduit between the outer surface of the elongate body and the inner surface of the fluid conduit sheath and; transporting fluid through the fluid conduit external to the elongate body.
 13. The method of claim 12, wherein the tool further comprises an electrical component and wherein the fluid conduit sheath is configured to direct fluid near the electrical component to cool the electrical component.
 14. The method of claim 13, wherein the electrical component comprises an electric motor configured to cause the gripper assembly to move between its actuated position and its retracted position. 